1. Field of the Invention
The present invention relates to a device for preventing toner from flying out of a developing device and a copier, printer, plotter, facsimile apparatus or similar electrophotographic image forming apparatus including the same.
2. Description of the Background Art
It is a common practice with an image forming apparatus to develop a latent image formed on an image carrier with a developer containing toner, transfer the resulting toner image to a sheet or recording medium, and then fix the toner image on the sheet for thereby producing a copy or a print. The problem with this type of image forming apparatus is that part of the toner not contributed to development flies out of a developing device via an opening for development. Such toner contaminates the inside of the apparatus or deposits on the image carrier and therefore on the sheet, lowering image quality. Moreover, the toner contaminates the portion of the developing device around the above opening and smears a person in the event of maintenance.
In light of the above, Japanese Patent Laid-Open Publication No. 10-3220, for example, discloses a toner scatter preventing device including a filter case on which a fan and a filter are mounted. A developing device adjoins a photoconductive element or image carrier and is formed with a suction port. The filter case with the fan and filter is mounted on the developing device around the suction port. The fan sucks air out of the developing device via the suction portion and discharges it via an exhaust port. As a result, air around the drum flows into the developing device via an opening for development also formed in the developing device, preventing toner from being scattered around via the opening. At the same time, the filter collects toner from air flowing toward the exhaust port.
However, the toner scatter preventing device described above has the following problems left unsolved. The toner collected by the filter accumulates on the filter little by little and obstructs the stream of air being sucked by the fan, thereby preventing the device from performing the expected operation. Further, the toner accumulating on the filter forms large masses in due course of time and drops into the developing device via the suction portion. Such masses of toner deposit on the drum and make the density of a toner image irregular, i.e., lower image quality.
Particularly, when use is made of toner with a small grain size for enhancing image quality including dot reproducibility and tonality, the toner implemented as fine powder is apt to fly about. Therefore, when an arrangement is made to suck the toner flying out of a developing device, the toner is collected in a great amount due to its small grain size and stops up a filter or fills up a tank in a short period of time. This results in the need for frequent maintenance including monitoring the time for replacement of the filter and that of the tank. Consequently, the above arrangement increases maintenance loads although enhancing image quality.
To solve the above problem, Japanese Patent Application No. 2001-168354, for example, proposes a toner scatter preventing device applicable to an image forming apparatus of the type using toner with a small grain size and constructed to reduce the amount of toner to fly about for thereby extending the interval between consecutive times of maintenance. The toner scatter preventing device is generally made up of exhausting means, toner collecting means, and toner storing means. The exhausting means exhausts air inside a developing device via an exhaust passage while the toner collecting means collects toner entrained by such air. The toner so collected is stored in the toner storing means without dropping into the developing device, so that a filter, for example, is prevented from being stopped up. In this case, use is made of a two-ingredient type developer containing toner having a weight-mean grain size of 65 xcexcm or below.
In the toner scatter preventing device described above, when the exhausting means exhausts air inside the developing device, air around an opening for development is sucked into the developing device while entraining flying toner into the developing device. More specifically, air is sucked into the developing device via the opening for development intervening between a developing roller and a case. However, air around opposite edges of the developing roller turns round into the developing device as well. This part of air makes the stream of air weaker at the opposite edges than at the center with the result that the opposite edges are more contaminated by scattered toner than the center. Although total suction may be intensified, it is difficult to intensity the stream of air at the opposite ends of the developing roller.
Application No. 2001-168354 stated above additionally proposes a configuration in which a suction port is positioned outside of and below the developing device, so that toner flying out of the developing device is sucked via the suction port. In this configuration, suction is intensified at portions outside of a sheet conveying range to thereby more intensely suck the toner flying out of the developing device. This, however, brings about another problem that the toner accumulates on the bottom of the developing device little by little and deposits on the image carrier in due course of time, smearing the resulting images. Moreover, this kind of scheme does not prevent the toner from flying out of the developing device, but simply sucks the toner flown out of the developing device.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 8-185046 and 10-274883.
It is an object of the present invention to provide a toner scatter preventing device capable of intensifying, when sucking air out of a developing device to thereby suck air around an opening for development formed in the developing device, intensifying air streams at both ends of the opening for thereby protecting the ends from smearing.
It is another object of the present invention to provide an image forming apparatus including a toner scatter preventing device with the above capability.
A toner scatter preventing device of the present invention is applied to a developing device configured to develop a latent image formed on an image carrier with toner. The toner scatter preventing device includes an exhausting section for exhausting air inside the developing device via an exhaust passage extending from the top of the developing device. An air stream generating device sucks air out of the developing device to thereby generate a stream of air that sucks air around an opening for development formed in the developing device. A suction port is formed in the developing device and communicated to the exhaust passage. The suction port is positioned outside of an image forming width assigned to the developing device.